Abstract

The dynamic regulation of cerebral blood flow (CBF) is thought to involve myogenic and chemoreflex mechanisms but the extent to which the sympathetic nervous system also plays a role remains debated. Here we sought to identify the role of human sympathetic neurovascular control by examining cerebral pressure-flow relations using linear transfer function analysis, and multivariate wavelet decomposition analysis that explicitly accounts for the confounding effects of dynamic end-tidal PCO2 (PETCO2) fluctuations. In 18 healthy participants randomly assigned to the 1-adrenergic blockade group (n=9; oral Prazosin, 0.05 mg/Kg) or the placebo group (n=9), we recorded blood pressure, middle cerebral blood flow velocity, and breath-to-breath PETCO2. Analyses showed that the placebo administration did not alter wavelet phase synchronization index (PSI) values while sympathetic blockade increased PSI for frequency components ≤0.03 Hz. Additionally, three-way interaction effects were found for PSI change scores, indicating that the treatment response varied as a function of frequency and whether PSI values were PETCO2-corrected. In contrast, sympathetic blockade did not affect any linear transfer function parameters. These data show that very low frequency CBF dynamics have a composite origin involving not only nonlinear and nonstationary interactions between BP and PETCO2, but also frequency-dependent interplay with the sympathetic nervous system.